Approximately 1.3 million osteoporotic fractures of the vertebrae hip, and distal radius occur each year in the U.S., with estimated annual costs in excess of $10 billion. Despite this, the biomechanics of the osteoporotic state have been little studied and controversy exists on the most suitable procedure to identify individual patients at high fracture risk. Until relatively recently, the most widely accepted screening procedure for osteoporosis was Single Photon Absorptiometry (SPA) to measure bone mineral content (BMC) of the distal radius. However, a number of studies have shown BMC of the distal radius to be a relatively weak predictor of fracture of the hip and spine and thus, in recent years, dual photon absorptiometry (DPA) and dual energy x-ray absorptiometry (DEXA) of the spine, hip, and total body and QCT of the spine have replaced SPA in many centers. Despite these trends, single photon absorptiometry remains an attractive option for clinical osteoporosis screening, primarily because of tits modest cost, low radiation dose, long-term precision, and large installed instrument base. In recent studies, we have identified biomechanical factors that we believe help explain the relatively poor performance of SPA of the distal radius to discriminate between fracture and non-fracture groups at remote skeletal sites. supported by an NIH Biomedical Resource Technology Program for Pilot Studies, we have developed a new Multiscan Single Photon Absorpitometry (MSPA) procedure for the distal radius which allows extraction of the necessary biomechanical information by performing multiple scans at varying angular orientations. Pilot experiments with cadaveric forearms have demonstrated highly significant improvements (when compared to conventional SPA) in the prediction of in-vitro failure loads necessary to simulate a Colles' fracture in-vitro. Our first objective in the proposed investigation will be to extend these pilot experiments to a sufficiently large sample to establish the precision and accuracy of the technique. Our second objective will then be to relate the MSPA measures and failure loads at the distal forearm to DEXA parameters and fracture loads for the proximal femora from the same cadaveric specimens. These correlations will test the hypothesis that radial MSPA parameters can be used to predict fracture risk at the proximal femur under controlled in-vitro loading conditions. And finally, to begin to explore the potential clinical applications of Multiscan Single Photon Absorptimetry, we will conduct a prospective comparison between MSPA parameters obtained at the distal radius and DEXA parameters obtained at the hip in patients being screened for osteoporosis. Through this comparison of non-invasive procedures applied at the wrist and hip, using a combination of in-vitro testing and clinical evaluation, we hope to provide a simple and inexpensive procedure which can be implemented on commercially available forearm scanners and thereby improve the discriminatory and diagnostic capabilities of single photon absorptiometry of the distal radius in the assessment of osteoporotic fracture risk.